Generally, a coating systems which is used in coating objects such as vehicle bodies or the like are constituted by a housing, an air motor which is mounted in the housing, a rotary atomizing head which is mounted on a fore end portion of a rotational shaft of the air motor, and a feed tube which supplied paint to the rotary atomizing head. In a coating system of this sort, the rotary atomizing head is put in rotation by the air motor, while paint is spurted into the rotary atomizing head through the feed tube, thereby spraying paint toward a coating object. In the course of a coating operation, it is usually the case that the paint color has to be changed frequently at multiple points for a number of coating objects which are successively transferred toward the coating system.
Therefore, recent developments in this field are focused on coating systems which necessitate to discard only a small amount of paint of a previous color on each color change and which can wash away deposited residues of previous color by the use of a reduced amount of solvent and within a short color changing time, for example, as disclosed in Japanese Laid-Open Patent Publication No. H6-134354 and H7-328493.
Prior art coating systems of this class are equipped with a plural number of paint feed tubes for the respective paint colors to be used, along with a solvent feed tube, and these feed tubes are extended axially and internally of the rotational shaft.
Accordingly, when changing the paint color, firstly the supply of paint of a previous color is stopped and then a washing solvent is spurted into the rotary atomizing head to wash away deposited residues of the previous color therefrom and to prepare for a coating operation in a new color without necessitating to discharge the previous color and without consuming a large amount of washing solvent.
Further, as another example of the prior art, there have been known the so-called cartridge type coating systems which are equipped with a plural number of paint cartridges which are filled with different paint colors and adapted to be replaceably mounted or loaded on a coating system, for example, as disclosed in Japanese Laid-Open Patent Publication No. H8-229446.
In the case of a cartridge type coating system just mentioned, one paint cartridge of a particular color which is selected from a number of paint cartridges of different colors is loaded into a housing of the coating system. Then, paint-extruding air is supplied to the paint cartridge from the side of the housing, thereby supplying paint in the cartridge to a rotary atomizing head of the coating system. At the time of changing the paint color, the paint cartridge itself is replaced by another cartridge of a desired color. Accordingly, it becomes unnecessary to omit a washing operation of a paint supply passage or passages, which has thus far been inevitably required on each color change.
The above-described prior art coating systems, having a plural number of feed tubes passed internally of a rotational shaft, need to place a multitude of feed tubes in the rotational shaft in order to cope with multiple paint colors.
However, it is difficult to place a large number of feed tubes in a rotational shaft of an air motor unless the diameter of the rotational shaft is large enough. It follows that the coating system needs to have an air motor of a large size, which would result in increases in size and weight of the coating system itself. For this reason, the coating system can usually receive only a limited number of feed tubes in the rotational shaft, thereby failing to cope with a large number of paint colors.
Further, in the case of the other prior art coating system of the cartridge type as mentioned above, it has been necessary to refill an unloaded paint cartridge each time when changing the paint color, and, for this purpose, it has been necessary to have paint refilling equipments located in the vicinity of the coating system for a paint refilling work, which is troublesome and time-consuming.